Effective magnetic moment of $Sc^{3+}$ ion is

The increase in the atomic radii of the third $(5d)$ series of transition elements is very small,which may be accounted for by the filling of '$X$' orbitals before '$Y$' orbitals. $X$ and $Y$ are:

Which of the following transition metal ions has a magnetic moment of $3.87 \ BM$?

The electronic configuration of gadolinium (atomic no. $64$) is

Why is the highest oxidation state of a metal exhibited in its oxide or fluoride only?

Which of the following elements is man-made (synthetic)?